Shallow Water Bathymetry Retrieval Using a Band-Optimization Iterative Approach: Application to New Caledonia Coral Reef Lagoons Using Sentinel-2 Data

Abstract

To achieve high accuracy bathymetry retrieval using remote sensing images with robust performance in a 0 to 25 m-deep lagoon with sharp bottom depth variations, a new Iterative Multiple Band Ratio (IMBR) algorithm is tested against known Multiple Band Ratio (MBR) and Single Band Ratio (SBR) algorithms. The test was conducted using the five multispectral bands, at 10 to 60 m resolution, of a Sentinel-2 image of the 25 km2 Poe lagoon, a UNESCO World Heritage Area. The IMBR approach requires training datasets for the definitions of depth threshold at which optimal band ratios vary. IMBR achieved accuracy, quantified with an original block cross-validation procedure across the entire depth range reached a mean absolute error of 46.0 cm. It compares very favorably against MBR (78.3 cm) and the various SBR results (188–254 cm). The method is suitable for generalization to other sites pending a minimal ground-truth dataset crossing all the depth range being available. We stress that different users may need different precisions and can use MBR or SBR algorithms for their applications. For the hydrodynamic modelling applications that are developing in New Caledonia, the IMBR solutions applied to Sentinel imagery are optimal.

Satellite-Derived Bathymetry for Selected Shallow Maltese Coastal Zones

“…The method proposed by [36] for deriving bathymetry from satellite imagery, which is based on a nonlinear solution and utilises band ratio calculations, was then used to compute the depth values. This method relies on the fact that the reflectance of two bands decrease exponentially with increasing depth [10]. The band with the shorter wavelength will attenuate less than the band with the longer wavelength.…”

“…These transitional, dynamic, and rapidly changing regions between land and water incorporate significant economic, social, and biological value which experience various pressures resulting from both natural and anthropogenic processes [8,9]. Understanding the submerged topography helps in achieving a number of marine related applications, for instance, realistic hydrodynamic 3D modelling, exploration of submerged landscapes and archaeological sites, coastal climate assessments [10], and port and waterway dredging, as well as resource management [11]. Bathymetry is at the forefront of coastal modelling, and thus, the availability of comprehensive depth information at various temporal and spatial scales is fundamental [12].…”

Hydrodynamic and hydrological processes within a variety of coral reef lagoons: Field observations during 6 cyclonic seasons in New Caledonia

“…In this area, the barrier reef complex lies directly in front of the shore, generating a shallow (< 4 m) lagoon of 25 km 2 , encompassing sandy terraces, patch reefs, and fringing reefs. The so-called "lagoon" is separated from the ocean with a continuous barrier reef at approximately 2 km from shoreline, only segmented by a narrow pass called "Shark fault" with an average depth of 25 m (Amrari et al, 2021).…”

Very High-Resolution Satellite-Derived Bathymetry and Habitat Mapping Using Pleiades-1 and ICESat-2

“…The method used to retrieve the map of the relative water depth could be improved to obtain more accurate DDM by implementing more recent and innovative approaches, such as IMBR, OBRA, MODPA or SMART-SDB [11,24,[57][58][59].…”